A Design Of Spin-Valve GMR Isolation Amplifier

Signal is transferred by isolation method between the measured object and monitoringequipment for safety and reliability in the application field of industrial control, high voltagemeasurement and medical equipment, etc. The isolator is a coupling device that communicatesindirectly between input and output section insulated in electrical, it transmits signal and restrainsnoise. The isolator plays a prominent part in data acquisition system with severe environmentconditions.The signals collected by sensor from the nature are weak analog signals, therefore it cannot befiltered, reshaped and other signal processing. Especially in data acquisition system with stronginterference noise, in order to improve the accuracy and reliability of data acquisition, must firstlyamplify gathered signal and restrain noise interference, and this work is completed by isolationamplifier. Isolation amplifier is a circuit that can amplify the input small signal and insulate it fromoutput. It has the characteristics of high common mode rejection ratio, good linearity and simplestructure, and usually is used in where digital signal isolator can’t.Transformer, capacitance and optoelectronic isolation amplifiers exist widely these days.Transformer and capacitive isolation amplifier have the good linearity, high precision, but lowbandwidth, high cost; compared with the former two, photoelectric isolation amplifier has higherbandwidth, but worse linearity. In addition, this paper designs a spin-valve giant magnetoresistance(GMR) isolation amplifier, it solves the problem that the three kinds of isolation amplifier abovecan’t have all of linearity, sensitivity and bandwidth, etc. It can completely replace the photoelectricand other isolation amplifiers.The task of this paper focuses on the external signal processing circuit design, mainly includesthe signal amplification circuit, V/I conversion circuit and receiving circuit, and make magnetic fieldsimulation and analysis for input coil about isolator. Based on CSMC0.5um mixed signal process,the circuit is edited, emulated and analyzed with the Tanner integrated circuit design software, andget the output current of the front-end signal processing circuit is3.6~10mA, the isolationamplifier gain is5, and other indicators basically meet the expected design requirements.